[time-nuts] T-bolt elevation error...

Michael Baker mpb45 at clanbaker.org
Sun Mar 30 08:50:31 EDT 2008


Hello, All--

Darrell Robinson said:

My guess is that at least some of the difference that you
see in your altitude is from the propagation delay in the
cable between your antenna and the GPS module.

Guessing still further, I would think that the position as
reported would be some distance immediately below the
antenna.  How long is your cable?
--------------------


Just for the sake of illustration, lets suppose that the
antenna is on my roof 20 feet above the ground but that
it took 150 feet of cable to get to the receiver.

Presumably, with no other information, the determined
altitude would be offset by the delay in the cable giving
a 130 foot error?

It would seem natural that the receiver would be (should be?)
able to be told how long the antenna cable is so that it
could factor out the delay.

However, I do not see any place in any of the control panels
to input a cable length correction.

Mike Baker
WA4HFR
Micanopy, FL



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